In wireless communications systems, such as long term evolution (LTE) systems, downlink and uplink transmissions may be organized into two duplex modes: frequency division duplex (FDD) mode and time division duplex (TDD) mode. The FDD mode uses a paired spectrum where the frequency domain is used to separate the uplink (UL) and downlink (DL) transmissions. FIG. 1A is a graphical illustration of an uplink and downlink sub-frame separated in the frequency domain for the FDD mode. In TDD systems, an unpaired spectrum may be used where both UL and DL are transmitted over the same carrier frequency. The UL and DL are separated in the time domain. FIG. 1B is a graphical illustration of UL and DL sub-frames sharing a carrier frequency in the TDD mode. In LTE-Advanced, carrier aggregation allows expansion of effective bandwidth delivered to a user terminal through concurrent utilization of radio resources across multiple carriers. Multiple component carriers are aggregated to form a larger overall transmission bandwidth. Carrier aggregation may be performed in LTE-Advanced TDD or LTE-Advanced FDD systems.
The following terms and abbreviations may be used throughout this disclosure:                ACK Acknowledgement        A/N ACK/NACK        ARI ACK/NACK Resource Indicator        BPSK Binary Phase Shift Keying        CA Carrier Aggregation        CC Component Carrier        CCE Control Channel Element        CFI Control Format Indicator        CP Cyclic Prefix        CQI Channel-Quality Indicator        CRC Cyclic Redundancy Check        DAI Downlink Assignment Index        DCI Downlink Control Information        DL DownLink        DwPTS Downlink Pilot Time Slot        eNB Evolved Node B        E-UTRA Evolved Universal Terrestrial Radio Access        FDD Frequency Division Duplex        FEC Forward Error Correction        GP Guard Period        HARQ Hybrid Automatic Repeat reQuest        IDFT Inverse Discrete Fourier Transform        IE Information Element        LTE Long Term Evolution (aka E-UTRA)        MAC Medium Access Control        MIB Master Information Block        NACK Negative Acknowledgement        OCC Orthogonal Cover Code        OFDM Orthogonal Frequency Division Multiplexing        PBCH Physical Broadcast Channel        PCFICH Physical Control Format Indicator Channel        PHICH Physical Hybrid-ARQ Indicator Channel        PCell Primary Cell        PDCCH Physical Downlink Control Channel        PDSCH Physical Downlink Shared Channel        PMI Precoding-Matrix Indicator        PRACH Physical Random Access Channel        PUCCH Physical Uplink Control Channel        QPSK Quadrature Phase Shift Keying        RACH Random Access Channel        RF Radio Frequency        RS Reference Sequence        RI Rank Indicator        RNTI Radio Network Temporary Identifier        SCell Secondary Cell        SFN System Frame Number        SIB1 System Information Block Type1        SPS Semi-persistent Scheduling        SRS Sounding Reference Signal        TDD Time Division Duplex        TTI Transmission Time Interval        UCI Uplink Control Information        UE User Equipment        UL UpLink        UpPTS Uplink Pilot Time Slot        